Describing, understanding, and explaining subjective experience in depression is a great challenge for psychopathology. Attempts to uncover neurobiological mechanisms of those experiences are in need of theoretical concepts that are able to bridge phenomenological descriptions and neurocognitive approaches, which allow us to measure indicators of those experiences in quantitative terms. Based on our own on going work with patients who suffer from depersonalization disorder and describe their experience as flat and detached from self, body, and world, we introduce the idea of phenomenal depth as such a concept. Phenomenal depth is conceptualized as a dimension inherent to all experiences, describing the relatedness of one's self with one's mental processes, body, and the world. More precisely, it captures the experience of this relatedness and embeddedness of one's experiences, and it is thus a meta- or secondorder experience. The psychopathology of DPD patients can be understood very generally as an instance of reduced phenomenal depth. We will argue that similar experiences in depression can also be understood as a reduction in phenomenal depth. We relate those ideas to neurocognitive studies of perception, emotion regulation, and the idea of predictive coding. Finally, we will speculate about possible neurobiological underpinnings of the dimension of phenomenal depth